Drugs that inhibit two enzymes in HIV-1, reverse transcriptase and protease, are the mainstays for treating HIV infection. In contrast, no approved drug exists to inhibit integrase, the third enzyme in this virus. In 1990, an in vitro enzymatic assay for purified integrase was developed called the 'strand-transfer assay'. Over the ensuing 11 years, at least 5 companies have tested over 1 million compounds using this assay, but only two have advanced to human testing. At the same time, studies on the HIV-1 preintegration complex (PIC) have demonstrated that it contains both viral and host cell proteins that are essential for its activity. This suggests that drugs could be developed that target the interactions between the host cell and the viral components in PICs. In this Phase I SBIR application, three Specific Aims are proposed to assess the applicability of a novel in vitro PIC assay for use in drug discovery. Aim 1 will identify the best method to make large amounts of PICs for use in the assay. Aim 2 will optimize the new PIC assay for high through put screening (HTS). Aim 3 will evaluate this HTS PIC assay using drug-like compounds in order to assess the feasibility of performing a large screen. When these studies are complete, it should be possible to begin developing drugs that block HIV-1 replication by inhibiting the PIC. Such drugs could become a new modality for treating HIV infection.